This novel 3-year R01 application focuses on a pilot clinical trial of peptide-based immunotherapy for ependymomas, among the most challenging childhood brain tumors. Although approximately 50% of tumors are cured with surgery and irradiation, a similar percentage of tumors recur and progress inexorably despite subsequent therapies. Affected children often experience cumulative morbidity from these interventions, before succumbing to refractory tumor progression. Accordingly, new treatment approaches are needed that target the unique features of these tumors. During the last decade, we have gained significant preclinical and clinical experience with immunotherapy for adult and pediatric astrocytomas, and propose to extend these insights to the treatment of childhood ependymomas, based on our observation that ependymomas frequently express high levels of specific tumor-associated antigens (TAAs), particularly IL13R2, EphA2, and survivin, often far exceeding levels we have observed in astrocytic tumors, which suggests that these tumors may be exceptionally promising candidates for immunotherapy. Building upon these data, we propose the use of a TAA-based vaccine cocktail, combined with an immunoadjuvant (imiquimod), for children with recurrent ependymomas. Because tumor location may have a strong impact on the potential for symptomatic immune- mediated tumor swelling (i.e., pseudoprogression), if there is a robust intratumoral immune response, the study will incorporate separate strata for posterior fossa and non-posterior fossa ependymomas. We will treat a total of 12 patients in each of the two strata with subcutaneous TAA epitope vaccinations every 3 weeks for 8 courses combined with topical imiquimod. Participants will be evaluated for adverse events, regimen limiting toxicity (RLT), and treatment response by clinical and laboratory evaluations and MR imaging. Participants who demonstrate disease stabilization or regression without RLT may receive additional vaccinations. These studies take advantage of unique institutional resources provided by our Immunologic Monitoring Laboratory, which are integrated into the clinical trial. We hypothesize that vaccine-based immunotherapy will not only prove safe for the treatment of pediatric ependymomas, but will also demonstrate activity as assessed by immunologic and clinical parameters. To address our hypotheses, we propose studies with the following aims: 1) To determine safety and tolerability of vaccination with TAA epitope peptides for children with recurrent ependymomas; and 2) To define the rate and magnitude of immune response in post-vaccine peripheral blood mononuclear cells against vaccine peptides, using IFN--enzyme-linked immuno-spot (ELISPOT) and tetramer assays. Preliminary data will also be obtained regarding clinical and imaging responses to therapy, associations between TAA expression and response, and mechanisms contributing to tumor resistance to immunotherapy. The results from this study, which would be the first vaccine-based trial conducted for ependymomas, will allow us to determine whether a subsequent larger phase II trial is warranted for these tumors.